In current cancer treatments, after many cancer tissues as possible are surgically removed, the remaining cancer cells are killed by radiotherapy and chemotherapy. This is currently the main method to treat tumors. But surgery has several problems, such as the removal range is broad and there is a recurrent risk by micrometastasis. Radiotherapy and chemotherapy also have many side effects. Especially, in the case of anti-tumor drugs, they are not always effective in all types of cancer. In many cases, remaining cancer cells that were exposed to an anticancer drug have a resistance to it, keep on growing and even metastasize to other organs. In the result, the cancer is impossible to fully treat.
Accordingly, there is a limit to overcome cancer using only these therapies. Therefore, immunotherapy is now being looked at as a new cancer treatment, which uses the immunity of our body.
Immunotherapy has side effects, but they are less severe than other treatments and is more effective in being used in combination with other treatments. Thus is the importance of immunotherapy. Immunotherapy is an indirect treatment that treats cancer by activating a patient's immune response whereas surgery, chemotherapy and radiotherapy directly attack cancer cells.
Broadly, the different types of immune responses fall into two categories: a humoral immune response and a cell-mediated immune response. The humoral immune systems function to make antibodies for degradation and removal of antigens, e.g. infectious microbes, viruses and bacteria, invading the human body. Meanwhile, the cellular immune response relates to immune surveillance mechanisms and produces cells (lymphocytes) specific to any antigen (cancer cell). The cellular immune response is more important than the humoral immune system in tumor-related immunity. Like this, antitumor immune response is generally related to cell-mediated responses; therefore it is known that the role of CD8+ cytotoxic T lymphocyte is important for this reaction. Nowadays, a tumor-associated antigen (TAA) has been studied to induce antitumor T cell. Also, the researches for T cell immunotherapy against tumor have been continued according to development of recombinant DNA technology.
As one of these attempts, U.S. Pat. No. 5,698,530 disclosed “a recombinant virus comprising a vaccinia virus into which a carcinoembryonic antigen (CEA) gene is inserted which recombinant virus expresses CEA on the surface of cells infected therewith and which recombinant virus elicits a cell medicated immune response in vivo directed against CEA and cells expressing CEA”.
However, in case that the antitumor immune response is induced by recombinant virus in vivo and then it is adopted for treatment of patients suffered from cancers, there is a limit that it is insufficient to supplement weakened immunity of the patients. Therefore, there has been a requirement toward a development of more effective immunotherapy and especially, the method for inducing cytotoxic T lymphocytes in vitro.